This invention relates to an endless belt, to an endless belt photoconductor, an endless belt and roller structure, and to an image forming apparatus.
In the field of image forming apparatuses such as copying machines and printing machines, there are increasing needs for color-formation, high speed image formation, compact apparatuses and high durability. The use of a large diameter photoconductor drum may satisfy the needs for high speed image formation and high durability but the apparatus becomes unavoidably large in size. The use of an endless belt photoconductor, the shape of which can be easily changed by use of rollers, can solve the above problem.
The endless belt photoconductor generally has a photoconductor layer provided on a support made of an electrically conductive material such as a conductive polymer or a metal. Because of dimensional stability, a metal support is preferably used for an endless belt photoconductor for high speed image formation. An endless belt is supported by a plurality of rollers and adapted to run by rotation of drive roller or rollers. Since each of the rollers for supporting the endless belt is generally not perfectly uniform in diameter throughout the axial length thereof, in sphericity of the cross-sectional shape thereof and in straightness of the axis thereof, the endless belt is apt to laterally move or meander during running. A large lateral movement of the belt may result in disengagement thereof from the rollers and breakage thereof. Further, even when the amplitude of the lateral movement is small, image quality is deteriorated especially when the endless belt photoconductor is used for full color image formation in which a color image is produced by superimposing yellow, cyan and magenta images.
To cope with the problems of lateral movement, there are proposals in which guides are provided on an inside surface of the belt along opposite side edges. The guides are disposed such that at least one of the side walls is in engagement with a side end of at least one of the rollers by which the endless belt is supported. For example, Japanese Laid Open Publication No. S59-230950 proposes an endless belt having guides prepared by applying a hot melt adhesive to an inside surface of the belt along opposite side edges. The melt is then cooled and solidified. Because the guides are apt to deform during the cooling step, however, the thus prepared guides cannot prevent lateral movement of the belt for a long period of operation. Japanese Laid Open Publication No. H04-190280 discloses an endless belt having rubber guides having a specific thickness and a rubber hardness. When the belt is driven at a high linear speed, however, the guides are apt to deform and separate from the belt.
There is also proposed a different type of means for preventing lateral movement of the endless belt, in which a pair of ribs are provided on an inside surface of the belt along opposite side edges. The ribs are disposed for fitting engagement with grooves provided on outer periphery of drive rollers by which the endless belt is supported or for engagement with sloped portions provided at both side ends of drive rollers by which the endless belt is supported. For example, in Japanese Laid Open Publication No. 2000-131998, the inside surface of each of the ribs which is in contact with and bonded to the inner surface of the belt is roughened to have an average surface roughness Ra of at least 0.3 μm to improve adhesion between the rib and the belt. It has been found, however, that when the known endless belt is operated at a high linear speed of, for example, 80 mm/sec or more, there often occurs delamination or separation of the rib from the belt. Japanese Laid Open Publication No. 2000-132001 discloses an endless belt having a pair of ribs bonded to an inner surface of the belt along a side end of the belt. The outer surface of each of the ribs at which the rib is brought into contact with rollers is roughened to have an average surface roughness Ra of at least 0.3 μm to decrease friction therebetween. It has been found, however, that when the known endless belt is operated at a high linear speed of, for example, 80 mm/sec or more, there often occurs lateral movement of the belt. The above endless belt and roller mechanism is also disadvantageous in that it needs the formation of grooves or inclined portions on the rollers.